The NaOtBu‐catalyzed mixed 1,1‐diboration of terminal alkynes using the unsymmetrical diboron reagent BpinBdan (pin = pinacolato; dan = 1,8‐diaminonaphthalene) proceeds in a regio‐ and stereoselective fashion affording moderate to high yields of 1,1‐diborylalkenes bearing orthogonal boron protecting groups. It is applicable to gram‐scale synthesis without loss of yield or selectivity. The mixed 1,1‐diborylalkene products can be utilized in Suzuki–Miyaura cross‐coupling reactions which take place selectivly at the C–B site. DFT calculations suggest the NaOtBu‐catalyzed mixed 1,1‐diboration of alkynes occurs through deprotonation of the terminal alkyne, stepwise addition of BpinBdan to the terminal carbon followed by protonation with tBuOH. Experimentally observed selective formation of (Z)‐diborylalkenes is supported by our theoretical studies.

Reactive ortho-benzyne derivatives are believed to be the initial products of liquid-phase [4+2]-cycloadditions between a 1,3-diyne and an alkyne via what is known as a hexadehydro-Diels–Alder (HDDA) reaction. The UV/VIS...

We have investigated the cannibalistic self-trapping reaction of an ortho-benzyne derivativeg eneratedf rom 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction. Without adding anys pecific trapping agent, the highly reactiveb enzyne is trapped by anotherb isdiyne molecule in at least three different modes.W eh ave isolated and characterized the resulting products and performed high-level calculations concerning the reactionm echanism. During the cannibalistic self-trapping process, either aC Ct riple bond or an sp-sp 3 CÀCs ingle bond is cleaved. Up to seven rings and nine CÀCb onds are formed startingf rom two 1,11bis(p-tolyl)undeca-1,3,8,10-tetrayne molecules. Our experimentsa nd calculations provide considerable insight into the variety of reactionp athways which the ortho-benzyned erivative,g enerated from ab isdiyne, can take when reacting with another bisdiynem olecule.

With the rapid development of the hexadehydro-Diels-Alder reaction (HDDA) from its first discovery in 1997, the question of whether a concerted or stepwise mechanism better describes the thermally activated formation of orthobenzyne from a diyne and a diynophile has been debated. Mechanistic and kinetic investigations were able to show that this is not a black or white situation, as minor changes can tip the balance. For that reason, especially, linked yne-diynes were studied to examine steric, electronic, and radical-stabilizing effects of their terminal substituents on the reaction mechanism and kinetics. Furthermore, the influence of the nature of the linker on the HDDA reaction was explored. The more recently discovered photochemical HDDA reaction also gives ortho-arynes, which display the same reactivity as the thermally generated ones, but their formation might not proceed by the same mechanism. This minireview summarizes the current state of mechanistic understanding of the HDDA reaction.

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